This invention relates to an improvement in elevators and, in particular, to an improvement in hydraulically operated elevators.
Historically, all types of elevator systems have utilized heavy T-shaped beams for guide rails which serve to direct the elevator car along a vertical path of travel as it is raised or lowered in the hoistway. In the case of a cable operated system, the rails also serve as an important part of the emergency braking system. In the event of an overspeed condition, automatically actuated brakes mounted upon the car engage the rails and bring the car to controlled safe stops. In order to minimize bending or distortion of the rails during both normal and emergency operations, it has been found advantageous to place the rails within a vertical plane that passes through the center of gravity of the car. This, however, places the rails outside of the stiles which form the structural side members making up part of the elevator car frame. The hoistway must accordingly be relatively wide to accommodate the laterally juxtaposed members.
In order to conserve valuable shaft space, the stiles are typically formed of outwardly facing channels and the T-rails are situated inside the channel openings. Although this "wrap-around" construction saves space, it nevertheless requires that the elevator car be assembled in the field rather than being prefabricated in the shop and shipped as a unit to the point of installation. Field assembly seriously limits the amount of flexibility that can be used in the design and construction of elevator cars.
With the introduction of more sophisticated electrical controls and signalling devices, it has also been found that elevator hoistways are becoming exceedingly crowded with electrical wiring. Oftentimes the wiring is randomly dispersed throughout the shaft making it extremely difficult to trace. The wiring also poses a hazard not only to equipment but also to anyone forced to work in the shaft.
In the last twenty-five years or so, the hydraulic elevator has gained a great deal of popularity, particularly in regard to use in smaller buildings that are under ten stories high. In this type of system, the car assembly is attached directly to the piston of a hydraulic lifting cylinder and the piston, rather than cables, serves to raise and lower the car. Because the piston supports the entire weight of the car, there is no practical reason to place the guide rails at the center of gravity of the car. This practice, however, still persists. Furthermore, most hydraulically operated elevators operate without the benefit of counterweights. The hydraulic system therefore must provide the energy necessary to both lift and brake the car along with its cargo. Accordingly, a good deal of potentially recoverable energy is wasted or dissipated as heat in the hydraulics.